a) Field of the Invention
The present invention relates to a spindle motor which rotates a rotor loaded with an object to be rotated (e.g. a hard disk, an optical disk, a rotary polygonal mirror). More specifically, it relates to a technology in which a drive magnet is adhesively fixed onto a rotor yoke.
b) Description of the Related Art
A spindle motor is used to rotate a variety of disks, rotary polygonal mirrors, and many other objects to be rotated. A popular type of this spindle motor rotatably supports a hub, which is a rotor, having a loading surface, to be loaded with an object to be rotated around a fixed shaft. The rotor comprises a rotor yoke, which is made of a magnet, and a drive magnet, which is adhesively fixed onto the rotor yoke. When making a drive magnet of conventional technology with a bonded magnet made of magnetic powder with a binder resin, the surface of the bonded magnet is coated with an epoxy resin, then, is adhesively fixed onto the rotor yoke with an epoxy adhesive.
In conventional technology, an epoxy adhesive is used for bonding a bonded magnet and a rotor yoke for the following reasons:
the same epoxy type adhesive adheres stronger to the epoxy coated surface of the bonded magnet; and PA1 an epoxy adhesive can completely cure the magnet coating without presence of a special catalyst, thus preventing out gassing, which may be caused by the adhesive which is still under curing.
However, there is a strong demand for reduction of manufacturing cost of a spindle motor. If epoxy is the only source for an adhesive that can bond a bonded magnet and a rotor yoke as is the case in conventional technology, the time required for curing the epoxy adhesive is too long; this will be a problem in improving productivity.